Flanged connections are well known. Flanged connections are used to connect lengths of pipe. Typically a flange extends radially (i.e. perpendicularly away from axis of the pipe) at each end of each pipe section to be connected, so that the flanges on each end are parallel to one another. Normally each flange has apertures extending axially (i.e. parallel to the axis of the pipe) through the flanges to permit fixings such as bolts or threaded studs to be inserted through the flanges so that the flanges can be compressed together to seal the two ends of the pipe to one another. Typically, a resilient gasket seal is compressed between the opposing faces of the flanges, and can often be held in an annular groove in one or both of the faces of the flange.
This is a satisfactory method of connecting pipe ends, and many miles of pipelines and flow lines from many industries are connected in this manner. Pipelines and their connections are of course subject to degradation over time and flanged pipeline connections such as are described above typically suffer from bolt failure before the flanges and the gaskets reach the end of their usable lives. Therefore, remedial work on flanged pipeline connections frequently involves changing out existing bolts that have corroded. Often, removal of a bolt from a flanged pipe connection requires interruption of the flow through the pipe, which can have significant adverse economic consequences in the case of oil pipelines and other high value fluid transfer pipelines. Therefore, the industry has adopted various “hot bolting” methods where individual bolts or threaded studs are removed and replaced one at a time, while the pipeline remains an active fluid conduit with fluids passing through the connection being repaired. However, this can sometimes have significant challenges, as some bolts can easily be extracted from the flanged connection and replaced relatively quickly, whereas other bolts have corroded too much to be unscrewed, and need to be split or cut from the flanged connection. Removing excessively corroded bolts increases the time involved, and also risks disturbing the connection through the high forces applied to the bolts in order to try to free them.